FIELD OF THE INVENTION
The present invention relates to switching power converters and ,in particular, to systems
for DC-DC switching power converters adapted for improving its light load efficiency by
skipping pulses using a voltage mode control scheme along with an input voltage feed-
forward and also to achieve monotonic spectral composition. The light load operation
includes a charging cycle, when the input energy is pumped into the inductor and also the
load and one or more skipped pulses. Importantly, the invention reduces the frequency of
switching and thus reducing switching losses and improving of converter efficiency. The
system of the invention is thus directed to solving the problem of light load efficiency of a
DC-DC switching converter and importantly achieves the same without requiring the
sensing of either inductor current or load current and advantageously provides for
achieving monotonic spectral composition and improved efficiency over a wide range of
input voltage and load current.
BACKGROUND ART
It is well known in the prevailing art of control of power conversion apparatus and in
particular DC-DC switching power converters, that such apparatus is usually used for
conversion of a DC (direct current) voltage into a different, stable DC voltage with high
efficiency. These are often used in electronics instruments, mobile phones and computing
devices. The conventional switching power converter circuits comprises one or more
switching elements, such as the metal-oxide semiconductor FETs (MOSFETs), that
selectively couple a DC power source to an inductor, such that said inductor is periodically
charged and discharged to produce a DC output voltage. They also alternatively couple
and decouple a voltage source to a load. Either way, a substantial noise is generated due
to the high frequency load alterations, which needs filtering. Conventionally, an output
filter comprising an inductor and a capacitor, removes high frequency switching noise to
produce the desired average output voltage.
The common type of switching converters already in use in the related art comprise buck
converter, boost converter, buck/boost converter and fly back converters. During light load
conditions, a converter operates in the discontinuous conduction mode (DCM), when within

a clock period, the current through the inductor (inductor current) reaches zero at steady
state.
In spite of the variations in the supply voltage and the load current, a controller is
expected to maintain the average output voltage of the converter at a desired reference
value. It is also experienced in the related art that the pulse width modulation scheme
(PWM) for power control of switching power converters, the operation of which is based on
the fixed frequency, suffers from poor efficiency at light load because of the domination of
switching losses.
It is also known in the related art that the pulse frequency modulation (PFM) and the pulse
skipping modulation (PSM) are useful in improving light load efficiency. While a PFM
improves light load efficiency, the variable frequency operation causes difficulty in
designing an input filter which requires (i) sufficient attenuation at the switching
frequency, (ii) stability with the follow on regulator and (iii) minimum size of filter.
Thus there occurs problems with PFM operation due to the conducted EMI and instability
with undue performance degradation. Moreover, system modeling and analysis become
difficult. Also, it is known that usually a conventional PSM, with a fixed duty ratio suffers
from (i) reduction in efficiency and increase in ripple magnitude with an increase in either
the load resistance or the input voltage (ii) large overshoot during transient and (iii) an
abrupt change in the spectral composition for a very small change in either the load
resistance or input voltage.
Some prior attempts have been made in the field to improve the efficiency and eliminate
the limitation of load sensitive performance for power control of DC-DC switching
converters such as those in the prior patents described in the following paragraphs:
US 7245113 disclosed a voltage regulator comprising a voltage source for providing an
input voltage and circuitry for regulating the input voltage to provide an output voltage.
The circuitry for regulating the input voltage includes at least a high side switch and a low
side switch. A skip mode controller controls the high side switch and the low side switch in
order to minimize conduction losses and switching losses within the voltage regulator.
US 7075280 is a patent titled "Pulse-skipping PFM DC-DC converter using a voltage mode
control loop" that disclosed a pulse frequency modulation (PFM) unit controlling the upper

limit level and lower limit level for an output voltage of a DC-DC converter. A voltage
mode control loop uses the upper and lower limit levels in a feedback loop to generate a
control signal to enable and disable the converter circuit.
US 6803752 and US 6593724 are two cognate patents by Chen, Wei et al directed to poly
phase PWM regulator/converter with high efficiency at light loads that disclosed multi-
phase multi-channel voltage regulator having high efficiency at light loads is provided. The
regulator increases efficiency at light loads by shutting down a select channel of the
regulator. In addition, the regulator may place remaining channels in Burst Mode.
US 6100675 disclosed a switching regulator capable of increasing regulator efficiency
under light load. The switching regulator involves a reference voltage circuit for producing
a reference voltage; an error amplifier for entering thereinto the reference voltage and a
measuring voltage produced by subdividing an output voltage from the switching regulator
and for amplifying a difference voltage between the reference voltage and the measuring
voltage; an oscillator circuit for outputting an oscillator signal; a PWM comparator for
comparing an output voltage of the error amplifier with an output voltage of the oscillator
circuit; load detecting means for detecting an output load current; and means for varying
efficiency of the switching regulator in response to load conditions detected by the load
detecting means.
US 5745352 disclosed a DC-DC converter functioning in a pulse-skipping mode with low
power consumption and PWM inhibit. Switching losses in a DC-to-DC converter idling in a
pulse-skipping mode (PSM) are reduced by inhibiting any intervening turn-off command by
a PWM control loop of the converter for as long as the current through the inductor of the
converter remains below a minimum threshold value set by a dedicated comparator. The
method is implemented by employing a comparator with a certain hysteresis and by
logically masking the switching to logic "0" of a high frequency clock (switching) signal of
the converter for the entire period of time the current in the inductor remains below the
minimum threshold.
US 5420777 disclosed a switching type DC-DC converter having increasing conversion
efficiency at light load. The invention showed switching frequency 'f', gate to source
voltage of a switching FET, and the stray capacity of the FET are decreased at light load
period to increase conversion efficiency at light load. In another embodiment, no-load
current is decreased by increasing self-inductance of a smoothing choke at light load.

Thus it would be apparent from the above that none of the above cited prior arts were
directed to solve the problems relating to conventional PSM with a fixed duty ratio to avoid
reduction in efficiency, increase in ripple magnitude, large overshoot during transient or
abrupt change in the spectral composition for small change in either the load resistance or
input voltage.
In all the cases, apart from complexities for implementing them, there is either a problem
of variable frequency operation or a non-monotonic spectral composition. There has
therefore been a need in the existing art to developing a method and system for power
control of DC-DC converter wherein a monotonic spectral composition and improved
efficiency and ripple magnitude could be achieved for a wide range of light load current
and input voltage.
OBJECTS OF THE INVENTION
It is thus the basic object of the present invention to provide a system for controlling
power converter and in particular a DC-DC switching power converter and a method for its
operation, using voltage control mode of pulse skipping modulation (VCPSM) favouring
achieving monotonic spectral composition and improved efficiency for a wide light load and
input voltage range for the apparatus.
A further object of the present invention is directed to a switching power converter for
achieving improved efficiency and stable ripple magnitude for a wide range of load current
and input voltage with said efficiency improvement being obtained over a light load range
without the need for any current sensing device.
Another object of the present invention is directed to a system for DC-DC switching power
converter wherein the power controller is suitable for application in high frequency power
management ICs.
A still further object of the present invention is directed to a system for DC-DC switching
power converter wherein the spectral composition could be varied monotonically for a wide
parameter range with resultant reduced EMI problem.

A still further object of the present invention is directed to a system for DC-DC switching
power converter wherein power conversion would be based on VCPSM scheme favoring
avoiding large overshoot during power transient and also control abrupt change in spectral
composition for small change in load resistance or input voltage.
A still further object of the present invention is directed to a system for DC-DC switching
power converter directed to facilitate elimination of undesired repetitive mode transition
between the PWM and the PSM near some critical parameters.
A still further object of the present invention is directed to a system for DC-DC switching
power converter wherein the same controller can be used for the PSM as well as PWM
operations.
A still further object of the present invention is directed to a system for DC-DC switching
power converter wherein the nature of variation in efficiency and periodicity, could be
controlled through an adjustable voltage, feed-forward gain and the proportional gain only.
According to yet another object of the present invention directed to said VSPSM based
power control for the DC-DC switching power converter wherein the entire operation could
be synchronized with an external clock, hence favoring reduced EMI problem.
A still further object of the present invention is directed to a system for DC-DC switching
power converter wherein an output feedback loop is considered to involve the reference
voltage and the actual output voltage.
A still further object of the present invention is directed to a system for DC-DC switching
power converter wherein an input voltage feed-forward is used to enhance the range of
input voltage for the pulse skipping operation retaining improved efficiency over wide
range.
A still further object of the present invention is directed to a system for DC-DC switching
power converter involving the mechanism of skipping of one or more pulses to improve
light load efficiency for the power converter.

SUMMARY OF THE INVENTION
Thus according to the basic aspect of the present invention there is provided a system for
improving load efficiency of switching power converters comprising:
a switching power circuitry;
a voltage control circuitry adapted for light load efficiency by skipping pulses with said
light load operation comprising a charging cycle during which the input energy is pumped
into the inductor with the load and one or more skipped pulses; and
a fixed frequency external clock adapted to synchronize the entire operation of the said
converter.
Another aspect of the present invention is directed to said system comprising an input
voltage feed-forward adapted to enhance the range of the input voltage for the pulse
skipping operation and to retain improved efficiency for a wide range of the input voltage;
A further aspect of the present invention is directed to said system comprising an
adjustable voltage adapted to increase the number of skipped cycles, the value of the said
adjustable voltage being set off-line and maintained throughout, said external voltage
being linearly dependent on the reference voltage.
A still further aspect of the present invention is directed to said system wherein said pulse
skipping operation is adapted to start functioning during a clock period when the output
voltage is above some threshold voltage at the beginning of the same clock period, the
duty ratio of the charging cycle being controlled by a voltage mode control scheme along
with feed -forward paths of the input voltage and an adjustable voltage.
A still further aspect of the present invention is directed to said system wherein said
voltage controller comprises a proportional controller adapted to decide on nature of
periodic behavior thereby and its spectral characteristics and adapted to retain improved
efficiency for a wide light load range.

According to an important aspect directed to said system of the present invention wherein
the output voltage of the switching power converter circuitry is subtracted from the
desired reference voltage involving a summing block and the output of summing block
considered as the error voltage to decide the selective operation of the converter whether
to undergo a charging pulse or a skipped pulse.
A still further aspect of the present invention is directed to said system wherein the said
error voltage is modified by multiplying a proportional gain to thereby achieve a monotonic
spectral composition, and variation of efficiency with the variation in the load current.
A still further aspect of the present invention is directed to said system wherein said input
voltage feed-forward is obtained from the input voltage of the switching power converter
circuitry which is also multiplied by a feed-forward gain which is subtracted from the sum
of the adjustable voltage and modified error voltage involving a summing block, the
output of the summing block being compared with a ramp signal involving a comparator
means, the output of said comparator means is latched involving a latch circuit.
According to yet another aspect of the present invention is directed to said system wherein
the output of said latch circuitry is indicative of the PWM duty ratio, which provides for the
duty ratio of a charging pulse in the proposed pulse skipping operation.
A further aspect of the present invention is directed to a system comprising a PSM logic
means adapted to compare the output from the latch circuitry and the error voltage to
determine whether it would be a charging cycle or a skipped cycle.
A still further aspect of the present invention is directed to said system comprising
operatively connecting the output of said PSM Logic means to the switching means of said
power converter circuitry.
A still further aspect of said system comprising an hysteretic comparator adapted to isolate
the classical PWM operation, during high and medium load conditions, and the PSM
operation during light load conditions.
The present invention and its objects and advantages are described in greater details with
reference to the following accompanying non limiting illustrative drawings.

BRIEF DESCIRPTION OF THE ACCOMPANYING FIGURES
The objects and advantages of the present invention is illustrated in further detail in
relation to non-limiting exemplary illustrations as per the following accompanying figures
wherein:
Figure 1: is the schematic illustration of the conventional switching power control system
for DC-DC converter using pulse frequency modulation (PFM) technique under light load
for controlled output when the load/ input voltage variation exist/occur.
Figure 2: is the graphical presentation of the nature of control achieved in the light load
range of out put controlled voltage obtained using the conventional system of Figure 1.
Figure 3: is the schematic illustration of the system for DC-DC switching power converter
using voltage control based pulse skipping modulation (VCPSM) control technique
according to the present invention.
Figure 4: is the schematic illustration of the control waveform presented graphically for the
VCPSM system for switching power control for DC-DC converter according to the present
invention.
Figure 5: is the graphical illustration of the variation in efficiency with the operating
frequency using a pulse frequency modulation (PFM) operation;
Figure 6: is the illustration of the variation in efficiency with the number of skipped cycles
using a pulse skipping modulation (PSM);
Figure 7: is the illustration of the plot of efficiency variation with the load current using (a)
the present invention (VCPSM) and (b) a classical pulse skipping modulation technique,
respectively.
Figure 8: is the illustration of the comparison of variation in efficiency with the load current
for (a) a pulse frequency modulation technique, operating under an optimal switching

frequency, (b) a pulse skipping modulation technique, operating under an optimal number
of skipped cycles and (c) the proposed voltage controlled based loop controlled pulse
skipping modulation technique.
Figure 9: is the illustration of the graphical plot of Loop Gain of the voltage-controlled
pulse skipping modulation technique to the invention.
Figure 10 (a)-(d): is the representation of the spectral characteristics of the input current
of a buck converter for R=100 using (a) the proposed pulse skipping technique according
to the invention and (c) a classical pulse skipping technique at Vin=12.9 V; and (b) and (d)
represent the said characteristics corresponding to Vin = 12.916V, plotted against the
normalized switching frequency (Fnormal).
Figure ll(a)-(d): is the representation of the load transient response for Vin =12 and a
step change in load current from 150mA to 50mA and back, where (a) and (c) represent
the inductor current, and (b) and (d) represent the output voltage of the proposed pulse
skipping modulation technique of the present invention and classical pulse skipping
modulation technique, respectively.
Figure 12: is the graphical presentation of load transient using the present invention from
100 mA to 50 mA wherein the upper plot is for output voltage and the lower plot is for
inductor current.
Figure 13: is the graphical presentation of the experimental waveforms of the voltage
control mode pulse skipping modulated (VCPSM) buck converter at a load current of
50mA, wherein the upper one indicates the output voltage and the lower one indicates the
inductor current.
Figure 14: is the graphical presentation of the experimental waveforms of the proposed
pulse skipping modulated buck converter at a load current of 100mA, wherein the upper
one indicates the output voltage and the lower one indicates the inductor current.

DEATAILED DESCRIPTION OF THE INVENTION WITH REFERENCE TO THE
ACCOMPANYING FIGURES
The present invention relates to a switching power converter and, in particular, to a
system for improving the light load efficiency of a DC-DC converter by selectively skipping
pulses using a voltage mode control scheme along with an input voltage feed-forward. The
operation of the converter is in synchronization with a fixed frequency external clock, thus
resulting in reduced EMI problem. The light load operation comprises a charging cycle
when the input energy is pumped into the inductor and also the load, and one or more
skipped pulses. During light load conditions, the skipping of pulses reduces the switching
loss, thereby improving efficiency. The pulse skipping operation starts functioning during a
clock period when the output voltage is above some threshold voltage value at the
beginning of the same clock period. The duty ratio of the charging cycle is controlled by a
voltage mode control scheme along with feed forward paths of the input voltage and an
adjustable voltage. The voltage controller comprises a proportional controller, which
decides the nature of periodic behaviour, thereby its spectral characteristics. It also favor
retaining improved efficiency for a wide light load range. The input voltage feed-forward is
used to enhance the range of input voltage for the pulse skipping operation and also to
retain improved efficiency of the converter for a wide range of the input voltage. An
adjustable voltage is used to increase the number of skipped cycles so as to improve
efficiency. For adjustable voltage regulation, the adjustable voltage is made linearly
dependent on the reference voltage. Importantly, the present invention does not require
sensing of either the inductor current or load current, and also achieves improved
efficiency over a wide range of input voltage and load current. The present invention thus
improves the efficiency, ripple magnitude and spectral composition of a DC-DC converter
under light load condition. The working principle of the VCPSM scheme for the desired
switching power control has been verified using circuit simulation tool and also using test-
set-up and the efficiency plot under different operating conditions are plotted and analyzed
to assess performance and reliability of the system.
The voltage control mode PSM based switching power control system (VCPSM) of the
present invention and in particular the DC-DC switching power converter system
incorporates a pulse skipping modulation (PSM) scheme using a voltage mode controlled
loop. The scheme considers an output voltage feed-back loop comprising comparing a

reference voltage and the actual output voltage. A proportional controller is incorporated
to improve efficiency and spectral characteristics over a wide range of light load current.
PSM logic units compare and stabilize the output voltage. A monotonic spectral
characteristic can be achieved for a considerable range of the proportional gain derived
from the system. The above aspects and the manner of implementation of said output
control for a wide range of input voltage and load current at light load condition are
described in greater details with reference to the accompanying drawings as follows:
Reference is first invited to the accompanying Figure 1 that schematically illustrates the
conventional switching power control system for DC-DC converter using pulse frequency
modulation (PFM) technique under light load for controlled output when the load/input
voltage variation exist/occur. Said Figure 1 shows a DC-DC buck converter which converts
a DC input voltage 101 to a DC-DC output voltage 107 with a reduced magnitude, i.e.,
step down operation. There is a metal-oxide-semiconductor switch (MOSFET), and its drain
103 is connected to the input voltage 101 through a wire 102. There is one diode 104 of
which cathode is connected to the source 105 of the MOSFET, and also to an inductor 106.
The anode of the diode 104 is connected to the ground 110. A capacitor 108 is connected
across the load resistance 109, which may not be necessarily a resistive load. There are
two threshold voltage limits 113 (upper limit) and 118 (lower limit). In a PFM technique, if
107 is less than the lower limit 118, then the converter undergoes a series of charging
pulses with constant on-time. When it reaches the upper limit 113, the converter
undergoes skipping phase, i.e., no operation, and thereafter voltage 107 starts falling, and
the operation continues. The comparison of the output voltage 107 with their upper limit
113 and lower limit 118 is carried out using two comparators 114 and 119 respectively.
Such conventional PFM mode operation of the DC-DC converter suffers from the limitations
on account of problems due to the conducted EMI and instability with undue performance
degradation. Thus improvement in light load efficiency in such conventional systems is
subjected to difficulty and complexity of designing an appropriate input filter due to
variable frequency operation. The ripple magnitude is also significant in modulated voltage
output associated with non monotonic spectral composition.
Reference is now invited to the accompanying Figure 2, that shows the graphical
presentation of the nature of control achieved in the light load range of output controlled
voltage obtained using the conventional system of Figure 1. In the accompanying Figure 2,
the upper and lower dotted lines indicate 113 and 118 in Figure 1, respectively. If the

output voltage 107 is less than or equal to 118, it undergoes a series of charging pulses
with either fixed on-time or an adaptive on-time cycle. When the output voltage 107
reaches 113, it undergoes no operation, and 107 starts falling. In this prior art, the
operating frequency varies with the variation in the light load current and also the input
voltage 101. Therefore, it suffers from conducted EMI problem.
Reference is next invited to the accompanying Figure 3 which shows the schematic
exemplary illustration of the system for DC-DC switching power converter using voltage
control based pulse skipping modulation (VCPSM) control technique according to the
present invention. The present invention is applied in a dc-dc buck converter which
converts the input voltage 301 to an output voltage 309 with a lesser magnitude. Figure 3
shows a dc-dc buck converter wherein a dc input voltage 301 is converted to a dc-dc
output voltage 309 of reduced magnitude, i.e., undergoing a step down operation. There is
a metal-oxide-semiconductor switch (MOSFET), and its drain 303 is connected to the input
voltage 301 through a wire 302. There is one diode 306 of which cathode is connected to
the source 305 of the MOSFET, and also to an inductor 307. The anode of the diode 306 is
connected to the ground 312. A capacitor 310 is connected across the load resistance 311,
which may not be necessarily a resistive load. The output voltage 309 is subtracted from
the desired reference voltage 314 using a summing block 315, and the output of 315 is
the error voltage 317. This error voltage decides the operation of the buck converter
whether it will undergo a charging pulse or a skipped pulse. The error voltage 317 is then
modified by multiplying with a proportional gain 318, resulting in 319. This proportional
gain takes a major role in achieving a monotonic spectral composition, and variation of
efficiency with the variation in the load current. An adjustable voltage 320 is also
considered, which can be used to increase or decrease the number of skipped cycles
during a particular value of load current and input voltage. The value of 320 is set off-line,
and held constant throughout. An input voltage feed-forward is considered, which is
obtained by connecting the input voltage 301 using a wire 322, and multiplied by a feed-
forward gain 323. Now the feed-forward voltage 323 is subtracted from the sum of the
adjustable voltage 320 and modified error voltage 319 using a summing block 324. The
output 325 of the summing block is then compared with a ramp signal 327 using a
comparator 328. The ramp signal uses a saw-tooth waveform 326. The output 329 of the
comparator 328 is then latched using a latch circuit 330. The output 331 of latch circuit
330 indicates a PWM duty ratio, which is then used as the duty ratio of a charging pulse in
the proposed pulse skipping operation. The PSM logic block 332 uses 331 and 317, where

317 determines whether it would be a charging cycle or a skipped cycle, and 331
determines the duty ratio of the charging cycle. The output 333 signal of 332 is then
connected to the gate 304 of the MOSFET. However, an additional driver circuit has to be
incorporated between 333 and 304, which has not been shown here.
The embodiment of the present invention as illustrated in Figure 3 is synchronized with
the external clock as compared to an asynchronous operation using the prior art as shown
in Figure 1, hence the latter one suffers from conducted EMI problem. In the prior art, the
adaptation of upper threshold and lower threshold voltages in many cases require a digital
implementation for further improving efficiency. However, the present invention is simple
to implement, and is useful to achieve monotonic spectral composition, improved efficiency
and ripple magnitude by simply choosing the gain parameters properly.
The DC-DC power converter system according to the present invention incorporates a
pulse skipping modulation (PSM) scheme using a voltage mode controlled loop. The
scheme considers an output voltage feed-back loop comprising comparing a reference
voltage and the actual output voltage. A proportional controller is further incorporated to
improve efficiency and spectral characteristics over a wide range of light load current.
Importantly, for a considerable range of the proportional gain, a monotonic spectral
composition could be achieved.
According to an aspect of the invention directed to a system for improving the light load
efficiency of the DC-DC switching power converter system the input voltage feed-forward
is incorporated to the feed-back loop of the system to enhance the range of the input
voltage for the pulse skipping operation so as to favor retaining improved efficiency of
conversion over a wide range of input voltage. Light load efficiency is improved by
skipping one or more pulses. The skipping mechanism starts functioning if the output
voltage is exceeding the threshold voltage level at the beginning of a clock period when
the main switch remains off through out that clock period, usually termed as the skipped
cycle. An external adjustable voltage applied to vary the number of skipped cycles as per
requirement in order to improve the efficiency further. Said external voltage is made
linearly dependent on the reference voltage which is useful for adjustable voltage
regulation purpose.

Reference is next invited to the accompanying Figure 4 that illustrates graphically the
control waveform presented for the voltage controlled pulse skipping modulated (VCPSM)
system for switching power control for DC-DC converter according to the present
invention. In accompanying Figure 4, the top (v0), the middle (d1), and the lower (d)
graph plots indicate 309, 333, and 331 in Figure 3, respectively. It shows that if 309 is
less than or equal to 314 at the beginning of a clock, it undergoes a charging cycle when it
consider the duty ratio as obtained in 331 directly; otherwise it disable the MOSFET switch.
The decision of either a charging cycle or a skipped cycle, is always considered at the
beginning of every clock cycle, as indicated as T, 2T, 3T etc. Therefore, overall operation is
always synchronized with the clock frequency.
Importantly, the control signal is achieved by summing up all the feedback signals,
comprising the voltage loop followed by the controller, the input voltage feed-forward and
the adjustable voltage.
According to a further aspect of the present invention directed to the power control of the
DC-DC switching power converter, said control signal voltage adapted to be compared
with the ramp signal to generate the duty cycle of the charging cycle, and the operation is
similar to that of the pulse width modulation (PWM) based voltage mode control, operation
of which is based on the fixed frequency. The ramp signal generated through a voltage
controlled voltage source by considering the reference voltage as the control voltage and
thus favoring adjustable voltage regulation.
Advantageously also, in the system according to the invention, a hysteretic comparator is
used to isolate the classical PWM operation during high and medium load condition and the
PSM operation carried out during the light load condition facilitating avoiding repetitive
mode transition between the PWM and the PSM near some critical parameter values.
Accompanying Figure 5 and Figure 6 are the graphical presentation that illustrate to
justify that the light load efficiency of a dc-dc converter, though can be improved by either
reducing the operating frequency in case of a pulse frequency modulation (PFM) operation
or increasing the number of skipped cycles in PSM mode operation, degrades if it goes
beyond a limit in either of the cases. Therefore, in either cases, there should be an optimal
point where efficiency would be maximum.

Reference is now invited to the accompanying Figure 7 showing the plot of efficiency
variation with the load current using (a) the present invention following the VCPSM
technique, and (b) a classical pulse skipping modulation (PSM) technique, respectively.
The comparison of the two corresponding efficiency plot clearly indicate the improvement
achieved over the conventional PSM by way of introducing the voltage mode feed-back
control loop according to the present invention. It shows that the classical PSM results in
poor efficiency under very light load due to high switching loss and that appears to have
been improved by about 5% using VCPSM. The synchronous topologies improve the
efficiency further but the degree of improvement using VCPSM over the classical PSM
remain more or less the same over the light load current range used for such comparative
analysis.
Reference is now invited to the accompanying Figure 8 which is the illustration of the
comparison of variation in efficiency with the load current for (a) a pulse frequency
modulation technique, operating under an optimal switching frequency, (b) a pulse
skipping modulation technique operating under an optimal number of skipped cycles, and
(c) the proposed voltage controlled based loop controlled pulse skipping modulation
technique. It is apparent from the plot of efficiency for the VCPSM mode of control that a
small change in the load current has significant impact on improving the efficiency in light
load range.
Reference is now invited to the accompanying Figure 9 that illustrate the graphical Bode
plot of Loop Gain of the voltage controlled pulse skipping modulation(VCPSM) technique
according to the invention. The loop gain indicates that the two poles are far away and one
zero is very close to the high frequency pole. Moreover, the closed loop system has an
infinite gain margin and a 90° phase margin. Hence the regulation in the output voltage
and the transient performance will be significantly improved using VCPSM.
The VCPSM scheme for power control of the DC-DC switching power converter according to
the present invention has been simulated using standard simulation software tools and
also physically tested using light load condition to validate the improvements in efficiency
of power/ DC voltage conversion as well as the spectral composition obtained using the
VCPSM system as of the invention as against the conventional PFM or classical PSM mode
of control.

Accompanying Figure 10 (a)-(d) is the representation of the spectral characteristics of
the input current of a buck converter for R=100Ω using (a) the proposed pulse skipping
technique according to the invention and (c) a classical pulse skipping modulation(PSM)
technique at Vin=12.9 V; and (b) and (d) represent the said characteristics corresponding
to Vln = 12.916V, plotted against the normalized switching frequency (Fnormalized).
Accompanying Figure ll(a)-(d) is the representation of the load transient response for
Vin =12 and a step change in load current from 150mA to 50mA and back, where (a) and
(c) represent the inductor current, and (b) and (d) represent the output voltage of the
proposed voltage control mode pulse skipping modulation(VCPSM) technique of the
present invention and classical pulse skipping modulation(PSM) technique, respectively.
Accompanying Figure 12 shows the graphical presentation wherein the upper plot is for
output voltage and the lower plot is for inductor current while subjected to load transient
from 100 mA to 50 mA ,using the system of the present invention. The variation in output
voltage justify proper regulation and response by the converter with high efficiency at light
load range.
Accompanying Figure 13 shows the graphical presentation of the experimental waveforms
of the proposed pulse skipping modulated buck converter at a load current of 50mA,
wherein the upper one indicates the output voltage and the lower one indicates the
inductor current.
Accompanying Figure 14 shows the graphical presentation of the experimental waveforms
of the proposed pulse skipping modulated buck converter at a load current of 100mA,
wherein the upper one indicates the output: voltage and the lower one indicates the
inductor current.
Figures 13 and 14 show the achievement of monotonic spectral composition practically
using the present invention.
It is thus possible by way of the above disclosed power control of the DC-DC switching
power converter to achieve the same without the need for any current sensing.
Importantly, improved efficiency and ripple magnitude are achieved for a wide range of
(light) load current and input voltages. Advantageously also, the same controller can be

used for the PSM as well as PWM operation. Furthermore, the nature of variation in
efficiency and periodicity can be controlled through an adjustable voltage, feed-forward
gain and proportional gain only.
The entire control operation is carried out in synchronism with the external clock with fixed
frequency; the current spikes caused by reverse recovery of the diode are suppressed and
finite slopes of the switching transitions achieved to overcome the limits on the problem of
conducted EMI.
The above illustrations clearly and sufficiently reveal the advantages residing in the
switching power converters and in particular to methods and systems for switching power
converters adapted for improving its light load efficiency by skipping pulses using a voltage
mode control scheme along with an input voltage feed-forward. Advantageously, the
invention favours by way of providing for the skipping of pulses during light load conditions
and thereby reducing switching losses and improvement of efficiency. It is also possible to
favour deciding between PFM and PSM mode operation and optimizing the number of
skipped cycles so as to improve/maximizing conversion efficiency. Thus the above
invention takes care of the problem of light load efficiency of a dc-dc converter and
importantly achieves the same without requiring the sensing of either inductor current or
load current and advantageously provides for achieving improved efficiency over a wide
range of input voltage and load current. The invention is thus suitable for a number of
electronic and computer devices and also the semiconductor industry, particularly
providing a monolithic controller IC for controlling dc-dc switching power converters,
mainly for light low power portable applications.

WE CLAIM:
1.A system for improving load efficiency of switching power converters comprising:
a switching power circuitry;
a voltage control circuitry adapted for light load efficiency by skipping pulses with said
light load operation comprising a charging cycle during which the input energy is pumped
into the inductor with the load and one or more skipped pulses; and
a fixed frequency external clock adapted to synchronize the entire operation of the said
converter.
2. A system as claimed in claim 1 comprising an input voltage feed-forward adapted to
enhance the range of the input voltage for the pulse skipping operation and to retain
improved efficiency for a wide range of the input voltage;
3. A system as claimed in anyone of claims 1 or 2 comprising an adjustable voltage
adapted to increase the number of skipped cycles , the value of the said adjustable voltage
being set off-line and maintained throughout, said external voltage being linearly
dependent on the reference voltage.
4. A system as claimed in anyone of claims 1 to 3 wherein said pulse skipping operation is
adapted to start functioning during a clock period when the output voltage is above some
threshold voltage at the beginning of the same clock period, the duty ratio of the charging
cycle being controlled by a voltage mode control scheme along with feed -forward paths of
the input voltage and an adjustable voltage.
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5. A system as claimed in anyone of claims 1 to 4 wherein said voltage controller
comprises a proportional controller adapted to decide on nature of periodic behavior
thereby and its spectral characteristics and adapted to retain improved efficiency for a
wide light load range.
6. A system as claimed in anyone of claims 1 to 5 wherein the output voltage of the
switching power converter circuitry is subtracted from the desired reference voltage
involving a summing block and the output of summing block considered as the error
voltage to decide the selective operation of the converter whether to undergo a charging
pulse or a skipped pulse.
7. A system as claimed in claim 6 wherein the said error voltage is modified by multiplying
a proportional gain to thereby achieve a monotonic spectral composition, and variation of
efficiency with the variation in the load current.
8. A system as claimed in anyone of claims 1 to 7 wherein said input voltage feed-forward
is obtained from the input voltage of the switching power converter circuitry which is also
multiplied by a feed-forward gain which is subtracted from the sum of the adjustable
voltage and modified error voltage involving a summing block , the output of the
summing block being compared with a ramp signal involving a comparator means, the
output of said comparator means is latched involving a latch circuit.
9. A system as claimed in claim 8 wherein the output of said latch circuitry is indicative of
the PWM duty ratio, which provides for the duty ratio of a charging pulse in the proposed
pulse skipping operation.
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10. A system as claimed in claim 9 comprising a PSM logic means adapted to compare the
output from the latch circuitry and the error voltage to determine whether it would be a
charging cycle or a skipped cycle.
10. A system as claimed in claim 9 comprising operatively connecting the output of said
PSM Logic means to the switching means of said power converter circuitry.
11.A system as claimed in anyone of claims 1 to 10 comprising an hysteretic comparator
adapted to isolate the classical PWM operation , during high and medium load conditions,
and the PSM operation during light load conditions.
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12. A system for improving load efficiency of a switching power converter substantially as
hereindescrtibed and illustrated with reference to the accompanying figures.

The present invention relates to a system for control of switching power converters adapted to improving the light load efficiency by skipping pulses using a voltage mode control(VCPSM) scheme along with an input voltage feed-forward and also achieving monotonic spectral composition and stable output for a wide range of input voltage and load current. The light load operation includes a charging cycle, when the input energy is pumped into the inductor (and also the load) and one or more skipped pulses. Importantly, the skipping of pulses during light load conditions reduce switching losses and improve efficiency of conversion. An adjustable voltage to favour increasing the number of skipped cycles so as to improve efficiency further. The system of the invention do not require any current sensing, reduced conducting EMI problem and improved ripple
magnitude, favoring wide scale application for a number of electronics and computer devices, semiconductor industry and in particular a monolithic controller IC for controlling dc-dc converters for light low power portable applications with economy and reliability.